We report on a paper-based analytical device (PAD) for the exhaustive, and therefore absolute, determination of halides in a range of diverse water samples and food supplements. A mixture of chloride, bromide, and iodide ions is assessed in a wide range of concentrations, specifically, from 10–4.8 to 0.1 M for bromide and iodide and from 10–4.5 to 0.6 M for chloride, with a limit of detection of 10–5 M. As a result of a careful optimization of the electrochemical cell, a thin layer made of cellulose paper (75-μm thickness), a cation-exchange Donnan exclusion membrane (FKL), and a silver-foil working electrode were selected as optimum materials. Cyclic voltammetry (from 0 to 0.8 V) was chosen as the interrogation technique to impose the exhaustive oxidative plating and re-reduction of halides on the silver element, accompanied by outward and inward counterion fluxes. The scan rate plays an important role in the ability of the technique to resolve mixtures of ions. Moderate scan rates (10 mV s–1) provide a suitable compromise between sensitivity, limit of detection, and resolution. This paper-based microfluidic device is extremely simple in terms of manipulation, cost, and contamination risk. Paper is an excellent basis for the establishment of a confined thin aqueous layer, the construction of disposable halide sensors, and portability for measuring outside the controlled laboratory environment. A discussion of the relevant analytical characteristics is presented herein, followed by a demonstration of halide assessment in water samples (sea, tap, river, and mineral waters) and food supplements enriched with iodide and chloride as early examples.